This invention relates generally to electrically illuminated display devices or signs, and more particularly to a sign including phosphorescent material having the capability of glowing for a substantial period after being exposed to ultraviolet radiation, incorporated into a system for cyclically recharging the phosphorescent material to maintain the light level produced by the glow at or above a given desired value.
It is well known that phosphor materials have the property of providing a visible glow while energized by a source of ultraviolet or blacklight radiation. Such phosphors exhibit afterglows whose light levels typically decay after removal of the energizing blacklight radiation. The rates of decay differs substantially among phosphors, and those preferred for use in the present invention have comparatively slow rates of decay, such as those including zinc sulfide activated by trace elements such as silver, copper or cadmium.
In accordance with the present invention, there is provided a sign having indicia which are desirably visible under ordinary illumination including sunlight, the indicia having the additional property of including slow-decaying phosphors similar to the types just mentioned. The present system includes an illuminating or activating light source, desirable in the form of an ultraviolet lamp such as a fluorescent lamp of known construction and characteristics. The system includes control means in the form of a photoelectric sensor responsive to the light level of illumination coming from the phosphorescent indicia, or a part thereof, and serving to energize the lamp when that light level decays below a predetermined value. The latter value will, of course, be established in accordance with the minimum desired visibility standard of the particular display involved. In the preferred form of the invention hereinafter described and illustrated, the photoelectric sensor serves in conjunction with a flasher of conventional construction to briefly energize the lamp and thereby to illuminate the phosphor material and thus recharge such material.
The display device of the present invention may include any suitable power supply adapted for producing power at the proper voltage and frequency for activating the lamp. Thus the power supply may be a dc source powered by batteries and including a conventional inverter for producing the necessary ac power, or the power suply may be fed from a conventional 60 cycle ac line. Alternatively, and particularly where the present device is used in an outdoor installation, a solar power generator is desirable and makes the entire installation independent of externally supplied power. Because the illuminating lamp is activated for only a short period of time during a cycle of recharging, the entire system is very economical in power consumption.
Accordingly it is a principal object of the present invention to provide and disclose a novel display device including a system for cyclically recharging the luminous material of the device. Other objects of the invention are to provide, in such a system, control means in the form of a photelectric sensor responsive to the light level emanating from a phosphor portion of a display device; to disclose in such a system a phosphor having a slow rate of decay of phosphorescence after removal of the exciting source of radiation; and for other and additional purposes as will be understood from a study of the following description of a preferred embodiment of the invention, taken in connection with the accompanying drawing.